1913.] Processes Operative in Solutions and Enzyme Action. 581 



and producible also by substances which must be inert in this respect. In 

 fact, a similar effect is produced whenever a substance is added which 

 increases the " osmotic tension " in the solution. Moreover, not only enzymes 

 butjall hydrolytic agents are affected. 



Thus Mr. Worley's experiments (S. XII) prove that the rate of hydrolysis 

 of cane sugar by acids is not proportional to the concentration of the former 

 at all strengths of the solution but soon reaches a maximum, as shown in the 

 following graph representing the results obtained with nitric acid in experi- 

 ments in which the sugar was the only variable : — 



430 

 ^ 420 



0-5 1-0 1-5 2 2-5 



Molecular proportions of sugar. 



These results, which correspond strictly with those obtaiued when the 

 concentration of the hydrolyte is varied relatively to an enzyme, are of 

 special importance as showing that the diminished activity must be due 

 to an alteration in the osmotic state — not to mechanical causes. 



That salts should retard hydrolysis by enzymes is only to be expected on 

 account of the " concentrating " effect they exercise. 



Neutral substances generally, however, also exercise an inhibiting effect 

 which not only varies according to the proportions in which they are 

 present but is also the greater the less soluble the substance. As slightly 

 or moderately soluble substances are often formed in cases of enzymic 

 hydrolysis this behaviour is of consequence. Eesults obtained with cane 

 sugar, illustrating the effect referred to, are given in No. XIII of the 

 Solution Studies and also in Nos. XI and XXV. It is shown that, in the 

 case of a considerable number of neutral substances used as precipitants 

 of salts, the less soluble precipitant is always the more efficient. It is 

 difficult to explain the effect they produce otherwise than by the assump- 

 tion that in presence of the neutral substance the water becomes more 

 active, in the sense that by their interposition the proportion of hydrone 

 molecules in the liquid is increased : consequently the degree of hydrolation 

 of any substances that may be present is lowered both because the solution 

 is more attractive and the surface therefore less attractive of hydrone and 

 because the neutral molecules also interfere directly at the hydrolated 

 surfaces and promote dehydrolation mechanically. The less they attract 

 hydrone and the more easily they can move about in the liquid, the more 



